The present invention relates to supercritical fluid extraction apparatus and particularly to a system for cleaning flow restrictors employed in such apparatus.
The use of supercritical fluid extraction is known for the analysis of the content of fat in samples. One such system that is commercially available is the FA-100 fat analyzer manufactured by Leco Corporation of St. Joseph, Mich. In this system, a carrier fluid such as liquefied carbon dioxide is heated under pressure from 31.degree. to 150.degree. C. to become a supercritical fluid that passes through a heated extraction assembly in which samples are placed. The supercritical fluid and solvated sample then flows through a flow restrictor, preferably a heated variable restrictor valve, and subsequently into a trap for the collection of fat contained in the sample. Although in the preferred embodiment heated variable restrictor valves are employed, other flow restrictors for the purposes of removing the fat content of a sample, such as capillary tubes or manually adjusted restrictor valves, can also be employed.
With such systems, the flow restrictor eventually becomes clogged with the sample material extracted, which is deposited in the restrictor until at some point in time it prevents the proper functioning of the equipment. It is necessary, therefore, to remove and clean the flow restrictors from the system on a schedule which is a function of how often the equipment is being used but can be required on at least a monthly basis. This requires an operator to disconnect and remove the flow restrictors from the system, clean the flow restrictors either mechanically or chemically or both, and subsequently reassemble the apparatus, resulting in significant cost as well as down time for the operation of the system.